If USB is the source, you have 500mA total between the board and the IO pin.

If Barrel jack is the source, then you have 800mA total between the board and the IO pin - and you may not reach that if the input voltage is high and regulator is dissipating a lot of heat: use a 7.5V source max if you have one.

The 5V reg is rated at 1 amp but the mega PCB heat sinking reduces this to about 200 mA. As James pointed out, it Strongly depends on the power source. The upper limit is about 17 volts and at a guess that input voltage would limit your output current to about 50 mA. The reason is that the board uses a linear regulator and it wastes the energy differential between power in and 5V as heat so the higher the input voltage the less current available as load power. You can safely run the regulator at 100 deg C (125 Deg C Max) but that isn't a real good practice. ideally the device wants to see about 7.6 - 7V... (1.1v max reg I/O differential + .7V for the series protection diode and an extra volt or so for "headroom" or a safety factor for pulsed loads, seems ideal or at least that is the way it works best for me. I use a 7V5 supply on my Arduino's and I haven't had any problems yet. You can use an external 5V source for your off board power requirements as well. Make sure though that you connect the board grounds together.

Bob

--> WA7EMS "The solution of every problem is another problem." -Johann Wolfgang von GoetheI do answer technical questions PM'd to me with whatever is in my clipboard

The actual header itself won't take 1A satisfactorily I fear - its not a high-current connector AFAIK. For high currents I'd recommend using an external regulator with suitable heat-sinking and high current wiring. Anyone have a reference to the actual datasheet for the headersused on Arduinos BTW?

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